Single vacuum debulk composite panel repair

ABSTRACT

A method of attaching a composite member to a structure. The method including forming a laminate of fabric impregnated with resin; applying heat at a first temperature to the impregnated laminate; applying vacuum at a first pressure to the impregnated laminate to degas the resin and form a degassed, impregnated laminate; positioning the degassed, impregnated laminate on a structure; and curing the degassed, impregnated laminate on the substrate by applying heat at a second temperature and by applying vacuum at a second pressure.

FIELD OF THE INVENTION

The present invention relates to the attachment of a laminate of fabricto a structure. In particular, illustrated embodiments of the presentinvention relate to providing fabric patches to composite structures,such as vehicles including helicopters.

BACKGROUND

U.S. Pat. Nos. 5,442,156 to Westerman et al.; 5,595,692 to Folsom etal.; and 4,659,624 to Yeager et al. are examples of composite structuresor repairs and each is incorporated herein by reference thereto in itsentirety, respectively.

SUMMARY OF THE INVENTION

One aspect of an embodiment of the invention is a method of attaching acomposite member to a structure, comprising: forming a laminate offabric impregnated with resin; applying heat at a first temperature tothe impregnated laminate; applying vacuum at a first pressure to theimpregnated laminate to degas the resin and form a degassed, impregnatedlaminate; positioning the degassed, impregnated laminate on a structure;and curing the degassed, impregnated laminate on the substrate byapplying heat at a second temperature and by applying vacuum at a secondpressure.

Another aspect of an embodiment of the invention includes a method ofattaching a composite patch to a structure to repair the structure,comprising: forming a laminate of fabric impregnated with resin; shapingthe laminate to correspond to an area of a structure needing repair;applying heat at a first temperature to the impregnated laminate;applying vacuum at a first pressure to the impregnated laminate to degasthe resin and form a degassed, impregnated laminate; positioning thedegassed, impregnated laminate on the area of the structure needingrepair; and curing the degassed, impregnated laminate on the areaneeding repair by applying heat at a second temperature and by applyingvacuum at a second pressure.

Another aspect of an embodiment of the invention includes a method ofattaching a composite patch to a structure to repair the structure,comprising: forming a laminate of fabric impregnated with resin; shapingthe laminate to correspond to an area of a structure needing repair;applying the laminate to the area of the structure needing repair;applying heat at a first temperature to the impregnated laminate;applying vacuum at a first pressure to the impregnated laminate to degasthe resin and form a degassed, impregnated laminate; and curing thedegassed, impregnated laminate on the area needing repair by applyingheat at a second temperature and by applying vacuum at a secondpressure.

Aspects, features, and advantages of this invention will become apparentfrom the following detailed description when taken in conjunction withthe accompanying drawings, which are a part of this disclosure and whichillustrate, by way of example, the principles of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings facilitate an understanding of the variousembodiments of this invention. In such drawings:

FIG. 1 illustrates a method in accordance with one embodiment of thesubject invention;

FIG. 2 illustrates a method in accordance with another embodiment of thesubject invention;

FIG. 3 illustrates a method in accordance with yet another embodiment ofthe subject invention;

FIG. 4 illustrates an exploded view of a curing schematic in accordancewith a further embodiment of the subject invention;

FIG. 5 illustrates a curing schematic in accordance with an embodimentof the subject invention; and

FIGS. 6-1 to 6-6 illustrate an embodiment of a repair process inaccordance with an embodiment of the subject invention.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates one embodiment of the present invention. Inparticular, FIG. 1 illustrates a method 10 of attaching a compositemember to a structure, including: forming a laminate of fabricimpregnated with resin 12; applying heat at a first temperature to theimpregnated laminate 14; applying vacuum at a first pressure to theimpregnated laminate to degas the resin and form a degassed, impregnatedlaminate 16; positioning the degassed, impregnated laminate on astructure 18; and curing the degassed, impregnated laminate on thesubstrate by applying heat at a second temperature and by applyingvacuum at a second pressure 20.

FIG. 2 illustrates another embodiment of the present invention. Inparticular, FIG. 2 illustrates a method 30 of attaching a compositepatch to a structure to repair the structure, comprising: forming alaminate of fabric impregnated with resin 32; shaping the laminate tocorrespond to an area of a structure needing repair 34; applying heat ata first temperature to the impregnated laminate 36; applying vacuum at afirst pressure to the impregnated laminate to degas the resin and form adegassed, impregnated laminate 38; positioning the degassed, impregnatedlaminate on the area of the structure needing repair 40; and curing thedegassed, impregnated laminate on the area needing repair by applyingheat at a second temperature and by applying vacuum at a second pressure42.

FIG. 3 illustrates a further embodiment of the present invention. Inparticular, FIG. 3 illustrates a method 50 of attaching a compositepatch to a structure to repair the structure, comprising: forming alaminate of fabric impregnated with resin 52; shaping the laminate tocorrespond to an area of a structure needing repair 54; applying thelaminate to the area of the structure needing repair 56; applying heatat a first temperature to the impregnated laminate 58; applying vacuumat a first pressure to the impregnated laminate to degas the resin andform a degassed, impregnated laminate 60; and curing the degassed,impregnated laminate on the area needing repair by applying heat at asecond temperature and by applying vacuum at a second pressure 62.

FIGS. 4 and 5 illustrate embodiments of tooling and materials that canbe employed to carrying out a particular embodiment of the invention,such as, for example, the methods illustrated in FIGS. 1-3 and theparticular embodiment of forming a repair patch as set forth in FIGS.6-1 to 6-6. The assembly 70 in FIG. 4 and the assembly 72 in FIG. 5relate to methods of repair or manufacture for a composite panel 74. Inparticular, the assembly 70 includes providing a vacuum device such as avacuum bag 76 and a heating device such as a heater blanket 78 for anon-site repair wherein a debulking or degassing cycle 16, 38, 60 isperformed to a repaired area 80 of composite material utilizing vacuumand applied heat prior to the curing stage 20, 42, 62, which includesthe application of vacuum and heat, but at increased levels relative tothe levels used during the degassing cycles 16, 38, 60.

One aspect to achieving the high quality of repair in the embodiments isthe use of a debulk cycle 16, 38, 60 prior to the curing phase 20, 42,62 of the repair. This allows any volatiles generated by the resin todegas from the patch 82 before the resin and fabric are consolidated forcuring. The result is a near void free, reproducible laminate 82 withoutclean room requirements or restrictions.

The embodiments described herein employ a curing step that debulks(degasses) the resin system under a low vacuum prior to applying fullcompaction (vacuum) pressure. Thus, a multi-step vacuum level combinedwith a multi-step temperature profile is one novel aspect of this newprocess.

The embodiments of FIGS. 4 and 5 produce an autoclave-quality compositerepair capable of being installed on-site, that is, at the vehicle beingrepaired, using only a vacuum bag 76 and a heater blanket 78. Otherprevious methods have employed autoclaves or dedicated equipment thatmade the repair difficult to make on-site, such as, for example, adouble vacuum debulk repair that uses dedicated tooling such as a rigidvacuum box. The assemblies 70 and 72 of the present invention, on theother hand merely use a collapsible vacuum bag 76 and a heating devicesuch as blanket 78. In the past, the part 80 would have to be scrappedor removed and sent to a repair facility for autoclave processing.

The embodiments of the invention are capable of producing anautoclave-quality composite repair merely using a vacuum bag 76 and aheater blanket 78. The method of the embodiments of the presentinvention permit the tools and materials to be readily available andeasily transported and the repair methods can be performed right on thestructure to be repaired, such as on-aircraft in the field while usingroom temperature storable materials (resin and fabric).

The method of the embodiment of the invention permit repairs to be doneon vehicles such as aircraft, at the aircraft's location. Additionally,repairs of structural parts are possible and since the laminates 82 ofthe embodiments are of autoclave quality, the thickness and weightrequired for any repair may be reduced. Further, the embodiments providepredictable laminate properties that can be calculated with areproducible process and the embodiments are especially helpful withthick laminates.

The illustrated embodiments of FIGS. 4 and 5 may relate to the repair ofcomposite parts for a vehicle, such as a helicopter or other structuresutilizing high quality composites (e.g., fiberglass and graphite). Inparticular, the repair methods disclosed herein are intended forcomposite repairs requiring restoration of load bearing properties.

FIGS. 6-1 through 6-6 illustrate in detail a proposed repair process 84in accordance with an embodiment of the invention. It should beunderstood that the process of FIGS. 6-1 through 6-6 is merely oneembodiment of the various embodiments that may formulate a repairprocess embodiment in accordance with the invention.

Referring to FIGS. 4, 5 and 6-1 through 6-6, a method and assembly isillustrated in particular for application to a helicopter and furtherfor repair of a structural composite part of a helicopter. In the repairprocess, a single patch 82 is formed to repair structure 74, which may apart of a helicopter. As stated in the repair process 84, templates areused to cut fabric, such as fiberglass or carbon fiber, in desiredshapes to address the area 80 of structure 74 needing repair (Steps7.1.1, 7.1.2). The fabric is impregnated with an appropriate resin andtogether the various layers of impregnated fabric are configured andstacked to form the appropriate laminate, which will form patch 82 (Step7.3). The number of layers of fabric forming the laminate of patch 82may vary depending on the specific structural requirements for eachparticular patch 82 application. For example, laminates having 4 to 24layers of fabric may be used in some applications.

The impregnated laminate 82 is positioned between layers of porousmaterial 86, such as porous Teflon and positioned on a nonporous layer88, which is itself positioned on stack of items including a heaterblanket 78 that is insulated by insulation 90 from base plate 92. A caulsheet 94 is positioned between the heater blanket 78 and the nonporouslayer 88 (Steps 7.2). A perforated nonporous layer 96 is secured by tape98 to the caul sheet 94 (Step 7.4.1). A breather layer 100 is positionedover the nonporous layer 96 and the vacuum bag 76 is sealed over theentire stacked assembly surrounding patch 82 and is secured in asubstantially air-tight manner to base plate 92 by a sealing elementsuch as sealant tape 102 (Step 7.4.6).

The heater blanket 78 is activated to heat patch 82 at a firsttemperature that is typically lower than the ultimate curingtemperature. As mentioned in Step 7.4.9 of FIG. 6-5, an example of afirst temperature is approximately 125 degrees (F) at a rate ofapproximately 3 degree (F) a minute while holding for approximately 90minutes if the patch is thicker than 16 plies, while a patch less than16 plies would hold the temperature for approximately 60 minutes whilemaintaining approximately 2 in. of Hg. On the other hand, an example ofa curing temperature may be approximately 200-250 degrees (F) at aheat-up rate of approximately 2-8 degrees (F) per minute.

At the same time as the first, degassing temperature is applied to patch82, a vacuum is drawn to a desired vacuum pressure that is typically notas great as the vacuum pressure drawn for ultimate curing of the patch82. As mentioned in Step 7.4.8 of FIG. 6-5, the vacuum bag 76 isconfigured to pull, through the use of conventional vacuum-formingapparatus, for example, approximately 2 inches of Hg for a patch 82 thatis 6 plies or greater. Then, during curing, typically a vacuum pressuregreater than that used during degassing will be employed to cure thepatch 82. Thus, a greater vacuum force is used for ultimately curing thepatch 82 on structure 74 than is used initially during degassing of thepatch 82.

The use of a vacuum and the application of heat on patch 82 acts todegas or debulk the patch and remove air including volatiles from thepatch 82. This degassing, which results in the removing of volatilesfrom the patch 82 help form a autoclave quality cure for patch 82.

Once the patch 82 as been heated and degassed sufficiently to remove airand other volatiles from the patch 82, the patch may be removed from thecaul sheet 94 while remaining attached to the porous layers (Step.7.4.11, FIG. 6-6). The patch 82 is then applied to the structure 74 asseen in FIG. 5 and vacuum pressure and heat is again applied to thepatch 82 to cure the patch 82. As mentioned above, a greater amount ofvacuum will be applied to the patch 82 as well as a higher degree ofheat for the ultimate curing of patch 82 as seen in FIG. 5.

The vacuum for the final curing may be provided by an appropriatevacuum-forming device such as a vacuum bag 76 attached to a vacuum andthe heat may be provided by a known heating device 104. The combinationof degassing the patch 82 as described above with vacuum and heat andthen curing the patch with vacuum and heat provide for a patch that issecurely attached to the structure 74 to the extent that the patch 82 isof the quality of patches that are provided to structures via anautoclave.

It should be understood that the specific amounts of vacuum and heatapplied will vary depending upon various factors, including the numberand type of fabric layers, the type and amount of resin used in formingpatch 82, and the other elements of the patch 82 and its application tothe structure 74.

Although FIG. 4 illustrates a situation where the patch is pre-formedand degassed on a base plate 92, e.g., for applications where a flatpatch 82 is needed, the base plate 92 may be contoured to match anydesired shape. Also, the patch 82 may be degassed while on the structure74, for example, in situations where the patch 82 may be needed to takea unique contoured configuration consistent with a contour of thestructure 74.

Also, although the more specific embodiments has described a compositepatch 82 that is attached to a composite structure 74, such as portionof a helicopter, the degassing of a composite structure, such patch 82,to improve the quality of the patch 82 as described herein may beapplied to any of the numerous situations outside of helicoptersrequiring such attachment of composite structures. For example, themethods herein are equally applicable to land or sea vehicle, especiallythose requiring repairs to structural members and those formed ofcomposite materials.

The foregoing embodiments have been provided to illustrate thestructural and functional principles of the present invention, and arenot intended to be limiting. To the contrary, the present invention isintended to encompass all modifications, alterations, and substitutionswithin the spirit and scope of the appended claims.

1. A method of attaching a composite member to a structure, comprising: forming a laminate of fabric impregnated with resin; applying heat at a first temperature to the impregnated laminate; applying vacuum at a first pressure to the impregnated laminate to degas the resin and form a degassed, impregnated laminate; positioning the degassed, impregnated laminate on a structure; and curing the degassed, impregnated laminate on the substrate by applying heat at a second temperature and by applying vacuum at a second pressure.
 2. A method according to claim 1, wherein the applying heat at a second temperature includes applying heat at the second temperature, which is greater than the first temperature.
 3. A method according to claim 1, wherein the applying vacuum at a second pressure includes applying vacuum at the second pressure to form a greater vacuum than that applied by the first pressure.
 4. A method according to claim 1, further comprising: positioning the impregnated laminate on a heating device.
 5. A method according to claim 1, further comprising: positioning a vacuum bag around the impregnated laminate.
 6. A method according to claim 4, further comprising: positioning a vacuum bag around the impregnated laminate.
 7. A method according to claim 1, wherein the applying vacuum is applied by a single vacuum enclosure.
 8. A method according to claim 7, wherein the applying vacuum is applied by a vacuum bag.
 9. A method of attaching a composite patch to a structure to repair the structure, comprising: forming a laminate of fabric impregnated with resin; shaping the laminate to correspond to an area of a structure needing repair; applying heat at a first temperature to the impregnated laminate; applying vacuum at a first pressure to the impregnated laminate to degas the resin and form a degassed, impregnated laminate; positioning the degassed, impregnated laminate on the area of the structure needing repair; and curing the degassed, impregnated laminate on the area needing repair by applying heat at a second temperature and by applying vacuum at a second pressure.
 10. A method according to claim 9, wherein the applying heat at a second temperature includes applying heat at the second temperature, which is greater than the first temperature.
 11. A method according to claim 9, wherein the applying vacuum at a second pressure includes applying vacuum at the second pressure to form a greater vacuum than that applied by the first pressure.
 12. A method according to claim 9, further comprising: positioning the impregnated laminate on a heating device.
 13. A method according to claim 9, further comprising: positioning a vacuum bag around the impregnated laminate.
 14. A method according to claim 12, further comprising: positioning a vacuum bag around the impregnated laminate.
 15. A method according to claim 9, wherein the applying vacuum is applied by a single vacuum enclosure.
 16. A method according to claim 15, wherein the applying vacuum is applied by a vacuum bag.
 17. A method according to claim 9, wherein the structure is a vehicle and the curing occurs with the impregnated, degassed laminate positioned on the vehicle.
 18. A method of attaching a composite patch to a structure to repair the structure, comprising: forming a laminate of fabric impregnated with resin; shaping the laminate to correspond to an area of a structure needing repair; applying the laminate to the area of the structure needing repair; applying heat at a first temperature to the impregnated laminate; applying vacuum at a first pressure to the impregnated laminate to degas the resin and form a degassed, impregnated laminate; and curing the degassed, impregnated laminate on the area needing repair by applying heat at a second temperature and by applying vacuum at a second pressure.
 19. A method according to claim 18, wherein the applying heat at a second temperature includes applying heat at the second temperature, which is greater than the first temperature.
 20. A method according to claim 18, wherein the applying vacuum at a second pressure includes applying vacuum at the second pressure to form a greater vacuum than that applied by the first pressure.
 21. A method according to claim 18, further comprising: positioning a heating device adjacent to the impregnated laminate.
 22. A method according to claim 18, further comprising: positioning a vacuum bag around the impregnated laminate.
 23. A method according to claim 21, further comprising: positioning a vacuum bag around the impregnated laminate.
 24. A method according to claim 18, wherein the applying vacuum is applied by a single vacuum enclosure.
 25. A method according to claim 24, wherein the applying vacuum is applied by a vacuum bag.
 26. A method according to claim 18, wherein the structure is a vehicle and the curing occurs with the laminate positioned on the vehicle. 